The broad goal of this project is to develop a protocol for quantifying the time course and amplitude of skeletal muscle perfusion and metabolic demand in the same volume of tissue in response to a standardized stress test. Our research plan is based on 3 key innovations: (1) the use of FAWSETS, an MR-based arterial spin labeling (ASL) technique we have developed specifically to overcome the limitations of other ASL techniques when they are used in skeletal muscle, (2) enhancement of FAWSETS through the use of custom- built gradients to reduce acquisition times and reduce SAR effects, and (3) the combination of gradient- enhanced FAWSETS with 31-P MR spectroscopy to examine the mechanistic links between local blood flow and cellular energetics during metabolic perturbation. All of our previous developmental work has been conducted in rat skeletal muscle. In SA#1 we will design and build the hardware and develop the protocols necessary to implement gradient-enhanced FAWSETS in human leg. In SA#2 we will combine our perfusion measurements with 31-P spectroscopy and test the ability of these tools to assess the cellular impact of impaired skeletal muscle perfusion in patients suffering from peripheral artery disease (PAD). Impaired skeletal muscle perfusion is observed in a variety of diseases, including insulin resistance and diabetes, congestive heart failure, compartment syndrome, PAD and systemic sclerosis. These diseases are serious public health issues that increase medical costs and reduce the quality of life for tens of millions of Americans. Currently, there is a nearly complete lack of accurate noninvasive methods for quantifying capillary-level perfusion in muscle, so the mechanistic links between impaired perfusion and exercise intolerance are poorly defined and not well understood. As a result, effective therapeutic interventions are limited and too often inadequate. Successful completion of this project will provide researchers and clinicians with a more detailed perspective from which to view these diseases and will have a major impact on the development of improved diagnostic techniques and therapies. [unreadable] [unreadable] [unreadable]